1. Field of the Invention
This invention relates to a stereomicroscope, and in particular, to a stereomicroscope used as a surgical microscope.
2. Description of Related Art
Stereomicroscopes are used in wide fields of researches, examinations, and surgical operations because minute parts of observation objects can be captured as three-dimensional images.
In the stereomicroscope, it is desired as one of main requirements to ensure a wide working space of a viewer. In particular, in the surgical microscope, besides ensuring a long working distance (WD) in order to obtain a working space for viewers (a chief operator and assistants), it is important to reduce a lateral dimension of an observation lens barrel. Specifically, in the surgical microscope, the viewer can ensure a wider substantial working space, for example, when an observation lens barrel 51′ shown in FIG. 1B is smaller in the lateral dimension than an observation lens barrel 51 shown in FIG. 1A, even though the working distances are identical.
In the stereomicroscope, optical factors determining the lateral dimension of the observation lens barrel are as follows:
(1) An internal inclination angle made by right and left observation optical systems (for eyes)
(2) A field angle of each observation optical system
(3) An NA (a numerical aperture) of each observation optical system
(4) An entrance pupil position of each observation optical system
However, that the internal inclination angle made by the right and left observation optical systems is made small becomes advantageous in reducing the lateral dimension of the observation lens barrel, but it impairs the performance of stereoscopic vision and thus is unfavorable.
Further, that the field angle of each observation optical system is made small becomes advantageous in reducing the lateral dimension of the observation lens barrel, but it narrows an observation range and thus is unfavorable.
Still further, that the NA of each observation optical system is made small becomes advantageous in reducing the lateral dimension of the observation lens barrel, but it darkens an observation image obtained through the observation optical system to degrade resolution and thus is unfavorable.
The entrance pupil position of each observation optical system varies with the arrangement of optical elements constituting the observation optical system. The lateral dimension of the observation lens barrel is affected by the entrance pupil position.
FIGS. 2A and 2B show relationships between the entrance pupil position of each observation optical system and the lateral dimension of the observation lens barrel in an arrangement that the entrance pupil position lies inwardly away from the top of the observation lens barrel and an arrangement that the entrance pupil position lies close to the top of the observation lens barrel, respectively.
In order to maintain the performance of favorable stereoscopic vision, it is necessary that the internal inclination angle made by the right and left observation optical systems, as mentioned above, is kept at a preset angle. Hence, in FIGS. 2A and 2B, the internal inclination angle made by the right and left observation optical systems is fixed at a preset angle θ so that the entrance pupil position is varied.
An arrangement that the entrance pupil position lies close to the top of the observation lens barrel as shown in FIG. 2B, in contrast with the arrangement that the entrance pupil position lies inwardly away from the top of the observation lens barrel as shown in FIG. 2A, requires less height of an off-axis chief ray at the top of the observation lens barrel, and therefore, the lateral dimension of the observation lens barrel can be reduced.
FIGS. 3A-3C and FIGS. 4A-4C show arrangement examples of common stereomicroscopes at low-magnification, middle-magnification, and high-magnification positions. Also, in FIGS. 3A-3C and FIGS. 4A-4C, only one optical system for the right eye is conveniently shown with respect to the stereomicroscope provided with optical systems for right and left eyes. In the optical system for the right eye, “R” is attached to a corresponding reference numeral, while in the optical system for the left eye, “L” is attached.
The stereomicroscope shown in FIGS. 3A-3C includes, in order from the object side, a single objective lens system 61; an afocal zoom optical system 62R (62L) which is one of a pair of right and left afocal zoom optical systems, located at a position decentered from the optical axis of the objective lens system 61; an aperture stop 63R (63L) which is one of a pair of right and left aperture stops, located at a position corresponding to the afocal zoom optical system 62R (62L); and an imaging lens system 64R (64L) which is one of a pair of right and left imaging lens systems, located at a position corresponding to the aperture stop 63R (63L). Also, in FIGS. 3A-3C, reference symbol FIR (FIL) represents an imaging position.
Here, in the case where observation is carried out by an optical microscope, an eyepiece system (not shown) which is one of a pair of right and left eyepiece systems is placed behind the imaging position FIR (FIL) which is one of a pair of right and left imaging positions, and an optical image formed through the imaging lens system 64R (64L) is observed through the eyepiece system. In the case of the observation by an electronic microscope, an electronic image sensor (not shown) which is one of a pair of right and left electronic image sensors is located at the imaging position FIR (FIL), and an optical image picked up by the electronic image sensor is converted into an electric signal so that an image displayed through a spectacles- or screen-type stereoscopic display device (not shown) is observed.
Also, in this description, a combination of optical elements ranging from the objective lens system to each of the imaging lens systems is referred to as the observation optical system.
The stereomicroscope of FIGS. 4A-4C is constructed so that the afocal zoom optical system of FIGS. 3A-3C is common to right and left optical systems, and has the single objective lens system 61; a single afocal zoom optical system 62; the aperture stop 63R (63L) which is one of a pair of right and left aperture stops, located at a position decentered from the optical axis of the afocal zoom optical system 62; and the imaging lens system 64R (64L) which is one of a pair of right and left imaging lens systems, located at a position corresponding to the aperture stop 63R (63L). An observation technique is the same as in FIGS. 3A-3C.
In the stereomicroscope of each of two conventional examples mentioned above, the aperture stop 63R (63L) is located relatively to the image side in the observation optical system, and the entrance pupil position of the observation optical system lies at a considerable distance away from the objective lens system 61 toward the image side. Consequently, the height of the off-axis chief ray passing through the objective lens system 61 is increased and in particular, reaches a maximum at the low-magnification position where the field angle becomes largest.
In conventional stereomicroscopes, unlike the stereomicroscopes shown in FIGS. 3A-3C and FIGS. 4A-4C, ones taking account of the entrance pupil positions are proposed, for example, in Japanese Patent Kokai Nos. 2006-158452 and 2006-194976.
The stereomicroscope set forth in Kokai No. 2006-158452 is constructed so that the entrance pupil position is made to lie between an objective optical system and an observation object (an object to be observed) and thereby favorable accommodation is obtained.
In the stereomicroscope set forth in Kokai No. 2006-194676, the object side of the observation optical system is designed to be telecentric so that the entrance pupil position of the observation optical system is made infinite, and in addition, an attempt is made to achieve compactness of the optical system.